Wireless control of lighting systems is increasingly replacing wired control, for example reducing installation costs and commissioning effort. A number of wireless technologies have been developed, including for example IEEE-802.15.4, Low-Power WiFi, WiFi, Bluetooth, EnOcean, Z-Wave and similar technologies, which typically permit short range communication.
For real-time control of a wireless lighting system, it is desired to minimize the latency when switching a state of the light source nodes of the lighting system. An example of such a lighting system is disclosed in US2006/0154598, where a group of light source nodes of a radio network are arranged to selectively respond to broadcast messages from a lighting system controller, thereby providing decreased latency for switching of the light source nodes.
However, in large-scale wireless lighting systems not all light source nodes may be in communication range with the lighting system controller. Rather, large-scale lighting systems require state-shift commands from the controller to the light source nodes to be routed also between the different light source nodes, effectively introducing different control command reception delays for the different light source nodes. Due to the nature of the different reception delays, the visual impression of the state-shift, such as wake-up or switch OFF lights, is unpleasant in that not all light source nodes shift state at the same time. For example, the CSMA/CA mechanism used with 802.15.4 or WiFi to access the wireless channel for transmitting a packet includes a random “backoff time” which will most probably be different on each node, causing some time/delay differences. Besides, collisions, different routes or different nodes with different processing power may cause some different delays.
Therefore, there is a need for an improved method that provides controlled state-shift in a wireless lighting system, having focus on obtaining a simultaneous state-shift of the light nodes.